8-bit I/O expander on the I2C bus
The PCA9534ADWR is an 8-bit I/O expander from Texas Instruments, communicating over I2C and SMBus at up to 400 kHz. It adds eight general-purpose I/O pins to a host controller with minimal bus overhead — each port can be configured as input or output, and the interrupt output (INT) signals the host when an input state changes, eliminating continuous polling.
Output drive and package fit
Each I/O pin can source 10 mA or sink 25 mA — enough to drive an LED directly or switch a small-signal relay through a transistor. The push-pull output stage eliminates the need for external pull-up resistors on output pins, though inputs remain high-impedance and require a pull-up for open-drain signals. Housed in a 16-SOIC package with a 7.50 mm body width (the wide-body variant), the PCA9534ADWR fits standard SOIC-16 footprints. The POR (power-on reset) feature ensures the I/O pins default to inputs on power-up, preventing unintended output states during supply ramp.